C++ standard libraries contains type_traits and iterator_traits defined in the libraries <type_traits> and <iterator> respectively. They are used heavily in 202204181536# and 202204182011# but soon deem unnecessary due to the introduction of #202203281200 in C++20.
You could get an #202202241727’s category by using the following alias:
template<typename Iter>
using Iterator_category_v = typename std::iterator_traits<Iter>::iterator_category;Template Deduction Guide is used to tell the compiler that the type of the passed parameter(s) should meet the requirement stated by the guide. It usually used alongside with #202204181611. Its replacement will be 202203281200# in C++20.
There are 5 categories of them which could be verified by 202204181611# :
The * operator could be used for variety of types without restriction. However, in order to use the operator ->, the type T has to be a class, specified from the #type predicate is_class.
When there is a need to execute a section of codes only when the type has met #some characteristics, compile-time if could be in great use. See the following examples:
C++(20) Concepts has superseded the functionalities from #202204181611, #202204181536 and #202204182011. It could be defined as follows using concept keyword: